Recently, cars that employ an AC motor as a power source for maneuvering the car and has an inverter apparatus mounted for driving the AC motor are becoming popular, as represented by electric cars, gas-electric hybrid cars and fuel-cell-powered cars.
For a car of such type, it is required to make smaller the driving apparatus that drives the AC motor with the inverter apparatus. The inverter apparatus generally consists of a switching element such as an IGBT (insulated gate type bipolar transistor) and a rectifying diode element. To attain smaller size, it is sometimes provided as a module. It is often the case that a capacitor for surge absorption is placed close to the switching element.
In a hybrid car that has severe cost and space restrictions, it is difficult to use a single part IGBT element and a single part capacitor element combined together, as such combination would increase cost and space.
Japanese Patent Laying-Open No. 2000-92847 discloses a semiconductor module apparatus with capacitor that realizes superior surge resistance performance. An external case of the semiconductor module fixes a smoothing capacitor while pressing the capacitor to a cooling base. Therefore, assembly and fixing of the capacitor can be simplified, while cooling characteristic of the capacitor can be assured.
According to the technology disclosed in Japanese Patent Laying-Open No. 2000-92847, the shapes of the capacitor and of a power module containing power elements such as the IGBT are adapted to facilitate assembly. The capacitor, however, is still fixed by screws to terminals of the power module. Therefore, there is still a room for improvement to make shorter the physical distance between the power element and the capacitor, and to reduce inductance component of the fixing portion. Further, the technology addresses attachment of the cooler only on one side of the power element, and therefore, there is still a room for improvement in view of cooling performance.
Further, better mileage is required of a hybrid car, and to meet the requirement, decrease in switching loss is essential. In order to decrease switching loss, switching at a higher speed than in the conventional art is necessary. High-speed switching, however, increases surge voltage generating at opposing ends of the switching element, making it necessary to add a snubber circuit.
A snubber circuit is for preventing a high spike voltage that generates in a state of transition at the time of switching, in a switching circuit that turns on/off the current flow. The spike current results from inductance component of lines on the current flow path, and it is particularly large at the moment when the switch turns off.
Typically, a portion where a power semiconductor is mounted and a portion where the capacitor of a snubber circuit is placed are apart by a distance, and these portions are connected by a bus bar. The bus bar, however, has inductance component, and hence, energy stored therein would undesirably be reflected as a surge voltage.